Fan

ABSTRACT

A fan includes blades and a motor. The motor includes a rotor holder; a shaft; a sleeve; a holder; and a thrust plate. A radial bearing portion arranged to support the shaft in a radial direction is defined in a radial gap defined between the shaft and the sleeve. A lower seal portion having a lower surface of a lubricating oil defined therein is defined between the thrust plate and the holder, while an upper seal portion having an upper surface of the lubricating oil defined therein is defined between the holder and the sleeve. The holder includes a connection channel defining portion arranged to define a connection channel to connect an upper space defined between the upper seal portion and an inside of the rotor holder with a lower space at which the lower seal portion is arranged.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fan arranged to produce an air current.

2. Description of the Related Art

Cooling fans arranged to cool electronic components have typically been installed inside cases of a variety of electronic devices. A fan motor disclosed in JP-UM-B 06-31199 includes a case, a stator, a sleeve, a shaft, an annular member, a rotor, and a plurality of blades. The stator is arranged on an outer circumference of an inner tubular portion of the case. The sleeve is fitted into the inner tubular portion and fixed thereto. The shaft is inserted in the sleeve. Grooves arranged to generate a dynamic pressure are defined in an outer circumferential surface of the shaft. The annular member is fitted on a lower end portion of the shaft and fixed thereto. The annular member is arranged axially opposite a lower surface of the sleeve. Each of a gap defined between the sleeve and the shaft and a gap defined between the sleeve and the annular member is filled with a lubricating fluid. The rotor is fixed to an upper end portion of the shaft. A magnet is fixed to an inner circumference of a cylindrical attachment member of the rotor, and is arranged radially opposite the stator. The blades are fixed to an outer circumference of the attachment member. In the fan motor, a radial dynamic pressure bearing is defined by a combination of the shaft and the sleeve, while a thrust dynamic pressure bearing is defined by a combination of the sleeve and the annular member.

During drive of a fan disclosed in JP-UM-B 06-31199, a difference in pressure may occur between an upper surface of the lubricating fluid, which is defined in the gap between the sleeve and the shaft, and a lower surface of the lubricating fluid, which is defined in a gap defined between a lower surface of the sleeve and an upper surface of the annular member or its vicinity. This pressure difference may cause a leakage of the lubricating fluid.

SUMMARY OF THE INVENTION

A fan according to a preferred embodiment of the present invention includes a plurality of blades and a motor arranged to rotate the blades about a central axis. The motor includes a stationary portion including a stator; a rotating portion including a rotor magnet arranged radially outside the stator; and a bearing mechanism arranged to support the rotating portion such that the rotating portion is rotatable with respect to the stationary portion. The rotating portion includes a rotor holder arranged in a shape of a covered cylinder, and including an outer circumferential surface on which the blades are arranged. The bearing mechanism includes a shaft; a sleeve in which the shaft is inserted; a holder arranged to hold the sleeve; and a thrust plate fixed to a lower end portion of the shaft on a lower side of the sleeve. The shaft and the sleeve are arranged to together define a radial gap therebetween, the radial gap including a radial bearing portion arranged to support the shaft in a radial direction. The thrust plate and the holder are arranged to together define a lower seal portion therebetween, the lower seal portion having a lower surface of a lubricating oil defined therein, while the holder and the sleeve are arranged to together define an upper seal portion therebetween, the upper seal portion having an upper surface of the lubricating oil defined therein. The holder includes a connection channel defining portion arranged to define a connection channel to connect an upper space defined between the upper seal portion and an inside of the rotor holder with a lower space at which the lower seal portion is arranged.

A fan according to another preferred embodiment of the present invention includes a plurality of blades and a motor arranged to rotate the blades about a central axis. The motor includes a stationary portion including a stator; a rotating portion including a rotor magnet arranged radially outside the stator; and a bearing mechanism arranged to support the rotating portion such that the rotating portion is rotatable with respect to the stationary portion. The rotating portion includes a rotor holder arranged in a shape of a covered cylinder, and including an outer circumferential surface on which the blades are arranged. The bearing mechanism includes a shaft; a sleeve in which the shaft is inserted; a holder arranged to hold the sleeve; and a thrust plate fixed to a lower end portion of the shaft on a lower side of the sleeve. The holder includes a cylindrical first holder arranged to cover an outer circumferential surface of the sleeve and an outer circumferential surface of the thrust plate, the first holder including an annular upper portion arranged to project radially inward on an upper side of the sleeve; and a second holder including an inner circumferential surface having an outer circumferential surface of the first holder fixed thereto, the second holder having the stator arranged on a radially outer side thereof. The shaft and the sleeve are arranged to together define a radial gap therebetween, the radial gap including a radial bearing portion arranged to support the shaft in a radial direction. The thrust plate and the first holder are arranged to together define a lower seal portion therebetween, the lower seal portion having a lower surface of a lubricating oil defined therein, while the shaft and the annular upper portion are arranged to together define an upper seal portion therebetween, the upper seal portion having an upper surface of the lubricating oil defined therein. The second holder includes a connection channel defining portion arranged to define a connection channel to connect an upper space defined between the upper seal portion and an inside of the rotor holder with a lower space at which the lower seal portion is arranged.

A fan according to yet another preferred embodiment of the present invention includes a plurality of blades and a motor arranged to rotate the blades about a central axis. The motor includes a stationary portion including a stator; a rotating portion including a rotor magnet arranged radially outside the stator; and a bearing mechanism arranged to support the rotating portion such that the rotating portion is rotatable with respect to the stationary portion. The stationary portion includes a bushing arranged to hold the stator on a radially outer side thereof. The rotating portion includes a rotor holder arranged in a shape of a covered cylinder, and including an outer circumferential surface on which the blades are arranged. The bearing mechanism includes a shaft; a bearing portion in which the shaft is inserted; a thrust plate fixed to a lower end portion of the shaft on a lower side of the sleeve; a thrust portion arranged to extend radially outward from an upper portion of the shaft; and a rotor cylindrical portion arranged to extend axially downward from the thrust portion. The shaft and the bearing portion are arranged to together define a radial gap therebetween, the radial gap including a radial bearing portion arranged to support the shaft in a radial direction. The thrust plate and the bearing portion are arranged to together define a lower seal portion therebetween, the lower seal portion having a lower surface of a lubricating oil defined therein, while the bearing portion and the rotor cylindrical portion are arranged to together define an upper seal portion therebetween, the upper seal portion having an upper surface of the lubricating oil defined therein. The bushing includes a connection channel defining portion arranged to define a connection channel to connect an upper space defined between the upper seal portion and an inside of the rotor holder with a lower space at which the lower seal portion is arranged.

According to preferred embodiments of the present invention, a reduction in a difference in pressure between the upper and lower spaces is achieved, and this contributes to preventing a leakage of the lubricating oil.

The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a fan according to a first preferred embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a bearing mechanism of the fan in an enlarged form.

FIG. 3 is a cross-sectional view illustrating the bearing mechanism in an enlarged form.

FIG. 4 is a horizontal cross-sectional view of the bearing mechanism.

FIG. 5 is a plan view of a thrust plate of the bearing mechanism.

FIG. 6 is a horizontal cross-sectional view of a holder according to a modification of the first preferred embodiment.

FIG. 7 is a cross-sectional view of a bearing mechanism according to another modification of the first preferred embodiment.

FIG. 8 is a cross-sectional view of a bearing mechanism according to yet another modification of the first preferred embodiment.

FIG. 9 is a cross-sectional view of a bearing mechanism according to yet another modification of the first preferred embodiment.

FIG. 10 is a horizontal cross-sectional view of a holder of the bearing mechanism illustrated in FIG. 9.

FIG. 11 is a cross-sectional view of a fan according to a second preferred embodiment of the present invention.

FIG. 12 is a cross-sectional view of a fan according to a third preferred embodiment of the present invention.

FIG. 13 is a cross-sectional view illustrating a bearing mechanism of the fan in an enlarged form.

FIG. 14 is a cross-sectional view of a bearing mechanism according to a modification of the third preferred embodiment.

FIG. 15 is a cross-sectional view of a fan according to a fourth preferred embodiment of the present invention.

FIG. 16 is a cross-sectional view of a fan according to a modification of the fourth preferred embodiment.

FIG. 17 is a cross-sectional view of a fan according to another modification of the fourth preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is assumed herein that a vertical direction is defined as a direction in which a central axis of a motor extends, and that an upper side and a lower side along the central axis in FIG. 1 are referred to simply as an upper side and a lower side, respectively. It should be noted, however, that the above definitions of the vertical direction and the upper and lower sides should not be construed to restrict relative positions or directions of different members or portions when the motor is actually installed in a device. Also note that a direction parallel to the central axis is referred to by the term “axial direction”, “axial”, or “axially”, that radial directions centered on the central axis are simply referred to by the term “radial direction”, “radial”, or “radially”, and that a circumferential direction about the central axis is simply referred to by the term “circumferential direction”, “circumferential”, or “circumferentially”.

First Preferred Embodiment

FIG. 1 is a cross-sectional view of an axial fan 1 according to a first preferred embodiment of the present invention. Hereinafter, the axial fan 1 will be referred to simply as the “fan 1”. The fan 1 includes a motor 11, an impeller 12, a housing 13, and a plurality of support ribs 14. The housing 13 is arranged to surround an outer circumference of the impeller 12. The support ribs 14 are arranged in a circumferential direction. The housing 13 and the motor 11 are connected to each other through the support ribs 14.

The impeller 12 is made of a resin, and includes a rotor holder 121 and a plurality of blades 122. The rotor holder 121 is substantially in the shape of a covered cylinder. The rotor holder 121 is arranged to cover an outer side of the motor 11. The rotor holder 121 is arranged to define a portion of a rotating portion 2 of the motor 11, which will be described below. The rotor holder 121 includes a top plate portion 123, a side wall portion 124, and a tubular bushing 125. The top plate portion 123 is arranged to spread perpendicularly to a central axis J1. The side wall portion 124 is arranged to extend downward from an outer edge portion of the top plate portion 123. The bushing 125 is made of a metal, and is fixed to a surface which defines a central hole of the top face portion 123. The blades 122 are arranged to extend radially outward from an outer circumferential surface of the side wall portion 124 with the central axis J1 as a center. The rotor holder 121 and the blades 122 are defined as a single member by a resin injection molding process.

The fan 1 is arranged to produce an air current traveling downward from above through rotation of the impeller 12 about the central axis J1 caused by the motor 11.

The motor 11 is a single-phase or three-phase motor of an outer-rotor type. The motor 11 includes the rotating portion 2, a stationary portion 3, and a bearing mechanism 401. The rotating portion 2 is supported by the bearing mechanism 401 to be rotatable with respect to the stationary portion 3. The rotating portion 2 includes the rotor holder 121, a substantially cylindrical metallic yoke 21, and a rotor magnet 22. The rotor holder 121 is arranged substantially in the shape of a covered cylinder. The yoke 21 is fixed to an inside of the side wall portion 124 of the rotor holder 121. The rotor magnet 22 is fixed to an inner circumferential surface of the yoke 21.

The stationary portion 3 includes a base portion 31, a stator 32, and a circuit board 33. The stator 32 is arranged on an outer circumference of the bearing mechanism 401. The stator 32 includes a stator core 321 and a plurality of coils 322 arranged on the stator core 321. The stator core 321 is defined by laminated magnetic steel sheets. The circuit board 33 is fixed below the coils 322. Lead wires from the coils 322 are attached to pins (not shown) inserted in holes of the circuit board 33, so that the stator 32 and the circuit board 33 are electrically connected with each other. Note that the lead wires from the coils 322 may be directly connected to the circuit board 33. During drive of the motor 11, a turning force is generated between the rotor magnet 22 and the stator 32, which is arranged radially inside the rotor magnet 22.

A Hall element 331 and a drive circuit (not shown) are mounted on an upper surface of the circuit board 33. The Hall element 331 is arranged under the rotor magnet 22 to detect changes in magnetic flux which accompany rotation of the rotor magnet 22.

A magnetic attraction force which attracts the rotor magnet 22 downward is produced between the rotor magnet 22 and the stator 32. This contributes to reducing a force that acts to lift the impeller 12 relative to the stationary portion 3.

The bearing mechanism 401 includes a shaft 41, an annular thrust plate 42, a sleeve 44, a thrust cap 45, i.e., a cap member, a holder 46, and a lubricating oil 47. The shaft 41 is inserted in the sleeve 44. An upper portion of the shaft 41 is fixed to the top face portion 123 through the bushing 125. Note that the upper portion of the shaft 41 may be directly fixed to the top face portion 123 without the bushing 125 intervening therebetween. The thrust plate 42 is fixed to a lower end portion of the shaft 41 on a lower side of the sleeve 44. The thrust plate 42 is arranged to extend radially outward from an outer circumferential surface of the shaft 41. The thrust plate 42 includes an inclined surface 421 defined between an outer circumferential surface and a lower surface thereof. The inclined surface 421 is arranged to be inclined radially inward with decreasing height.

The sleeve 44 is a metallic sintered body impregnated with the lubricating oil 47. The sleeve 44 is held inside the holder 46, which is substantially cylindrical in shape. The holder 46, the base portion 31, and the support ribs 14 are defined as a single member. The holder 46 is arranged to extend upward from a central portion of the base portion 31. The holder 46, the base portion 31, and the support ribs 14 are made of a resin. Note that the holder 46, the base portion 31, and the support ribs 14 may be made of a metal. An upper portion of the holder 46 includes an upper annular portion 461 and an upper cylindrical portion 462. The upper annular portion 461 is arranged in an annular shape centered on the central axis J1, and is arranged on an upper side of the sleeve 44. The upper cylindrical portion 462 is arranged to extend upward from an outer edge portion of the upper annular portion 461. The holder 46 further includes a connection channel defining portion 5. The connection channel defining portion 5 is arranged to define a connection channel 51 in the holder 46. A radially inner portion of the stator core 321 is fixed to an outer circumferential surface of the holder 46. Note that each of the shaft 41 and the thrust plate 42 defines a portion of the rotating portion 2, while each of the sleeve 44, the thrust cap 45, and the holder 46 defines a portion of the stationary portion 3.

FIG. 2 is a cross-sectional view illustrating a portion of the bearing mechanism 401 in an enlarged form. Each of an upper portion and a lower portion of the sleeve 44 is fixed to an inner circumferential portion of the holder 46. A portion of the inner circumferential portion of the holder 46 which is arranged to be in radial contact with the upper portion of the sleeve 44 will be hereinafter referred to as an “upper contact portion 463”. A portion of the inner circumferential portion of the holder 46 which is arranged to be in radial contact with the lower portion of the sleeve 44 will be hereinafter referred to as a “lower contact portion 464”. An outer circumferential surface of the sleeve 44 includes an inclined surface 441 arranged to be inclined radially inward with increasing height between the upper and lower contact portions 463 and 464.

An upper seal gap 611, which is arranged to gradually increase in radial width with increasing height, is defined between the inclined surface 441 of the sleeve 44 and an inner circumferential surface 46 a of the holder 46. An upper seal portion 61 a, which is arranged to retain the lubricating oil 47 through capillary action, is defined in the upper seal gap 611. An upper surface of the lubricating oil 47 is defined in the upper seal portion 61 a.

FIG. 3 is a diagram illustrating an upper portion of the fan 1 in an enlarged form. FIG. 4 is a cross-sectional view of the bearing mechanism 401 taken along line A-A in FIG. 3. The upper contact portion 463 of the holder 46 includes cut portions 463 a each of which extends in a vertical direction. Each cut portion 463 a is arranged to define an airway 651 extending in the vertical direction between the upper contact portion 463 and the outer circumferential surface of the sleeve 44. The airway 651 is arranged to bring the upper seal gap 611 into communication with a space 656 defined between an upper surface of the sleeve 44 and a lower surface of the upper annular portion 461.

As illustrated in FIG. 3, the bushing 125 is arranged above the holder 46. A horizontal gap 652 extending in directions perpendicular to the central axis J1 is defined between a lower surface of the bushing 125 and an upper surface of the upper annular portion 461. A vertical gap 653 extending in an axial direction is defined between an outer circumferential surface of the bushing 125 and an inner circumferential surface of the upper cylindrical portion 462. The vertical gap 653 is arranged in an annular shape centered on the central axis J1. The upper seal gap 611 is arranged to be in communication with a space above the stator 32 illustrated in FIG. 1 through the airways 651, the space 656, a gap defined between the shaft 41 and an inner edge of the upper annular portion 461, the horizontal gap 652, and the vertical gap 653. The upper seal gap 611, the airways 651, the space 656, the horizontal gap 652, and the vertical gap 653, that is, a space enclosed by the sleeve 44, the holder 46, the shaft 41, and the bushing 125, will be hereinafter referred to collectively as an “upper space 61”. Note that the upper space 61 may include a space defined in the vicinity of the vertical gap 653 between the rotor holder 121 and an inner circumferential portion of the stator 32 illustrated in FIG. 1.

As illustrated in FIG. 2, the thrust cap 45 is arranged in the shape of a disk, and is fixed to a lower portion of the holder 46 below the thrust plate 42. The thrust cap 45 is arranged to close a lower opening of the holder 46. The bearing mechanism 401 includes a space 62 enclosed by the thrust cap 45, the thrust plate 42, the holder 46, and the shaft 41. The space 62, which is defined above the thrust cap 45, will be hereinafter referred to as a “lower space 62”. A portion of the lower space 62 which is defined between the inclined surface 421 of the thrust plate 42 and the inner circumferential surface 46 a of the holder 46 will be referred to as a “lower seal gap 621”. The lower seal gap 621 is arranged to gradually increase in radial width with decreasing height. A lower seal portion 62 a, which is arranged to retain the lubricating oil 47 through capillary action, is defined in the lower seal gap 621. A lower surface of the lubricating oil 47 is defined in the lower seal portion 62 a.

The connection channel 51, which is defined by the connection channel defining portion 5, includes a vertical hole 511, an upper horizontal hole 512, and a lower horizontal hole 513. The vertical hole 511 is arranged to extend in the vertical direction in the holder 46. The upper horizontal hole 512 is arranged to extend radially inward from a top portion of the vertical hole 511. An end opening of the upper horizontal hole 512, i.e., an upper end opening of the connection channel 51, is defined in a middle portion of the inner circumferential surface 46 a of the holder 46. The upper horizontal hole 512 is joined to the upper seal gap 611 on an upper side of the upper seal portion 61 a. The lower horizontal hole 513 is arranged to extend radially inward from a bottom portion of the vertical hole 511. An end opening of the lower horizontal hole 513, i.e., a lower end opening of the connection channel 51, is defined in a lower portion of the inner circumferential surface 46 a of the holder 46. The lower horizontal hole 513 is joined to the lower space 62 on a lower side of the lower seal portion 62 a. In the bearing mechanism 401, the upper and lower spaces 61 and 62 are connected with each other through the connection channel 51.

A seal member 311, which is a nameplate, is attached to a lower surface of the base portion 31 on a lower side of the thrust cap 45. The fan 1 includes a space 622 enclosed by the seal member 311, a lower surface of the thrust cap 45, and an inner circumferential surface of the base portion 31. The space 622, which is defined below the thrust cap 45, will be hereinafter referred to as a “below-cap space 622”.

A thrust gap 64 arranged to extend radially is defined between an upper surface of the thrust plate 42 and a lower surface of the sleeve 44. FIG. 5 is a plan view of the thrust plate 42. The upper surface of the thrust plate 42 includes a thrust dynamic pressure groove array 641 arranged in a herringbone pattern. A thrust bearing portion 64 a arranged to generate, during the drive of the motor 11, a thrust dynamic pressure acting on the lubricating oil 47 through the thrust dynamic pressure groove array 641 is defined in the thrust gap 64.

A radial gap 66 arranged to extend in the axial direction is defined between an inner circumferential surface of the sleeve 44 and the outer circumferential surface of the shaft 41. A radial bearing portion 66 a arranged to generate a radial dynamic pressure acting on the lubricating oil 47 during the drive of the motor 11 is defined in the radial gap 66. As illustrated in FIG. 3, a top portion of the sleeve 44 includes an upper-side groove portion 442 arranged to extend radially. An upper plate 48, which is arranged in an annular shape, is arranged on the upper surface of the sleeve 44. A communicating channel 654 arranged to extend radially is defined between the upper-side groove portion 442 and the upper plate 48.

The communicating channel 654 serves to guide a portion of the lubricating oil 47 which soaks out of the top portion of the sleeve 44 into the radial gap 66, and also to prevent a leakage of the lubricating oil 47 through the top portion of the sleeve 44. Note that a portion of the lubricating oil 47 which is in the communicating channel 654 may sometimes flow toward the upper seal gap 611. In the bearing mechanism 401, a so-called labyrinth structure is defined by provision of the horizontal and vertical gaps 652 and 653. This contributes to preventing an air including a lubricating oil evaporated from an upper portion of the radial gap 66 from traveling out of the bearing mechanism 401, and to reducing evaporation of the lubricating oil 47 out of the bearing mechanism 401.

During drive of the fan 1 illustrated in FIG. 1, the thrust plate 42 is stably supported in the axial direction with respect to the stationary portion 3 through the thrust bearing portion 64 a, while the shaft 41 is stably supported in a radial direction through the radial bearing portion 66 a. Use of the bearing mechanism using fluid dynamic pressure in the fan 1 contributes to reducing a production cost of the fan 1 as compared to the case where a ball bearing is used therein, and also to reducing noise during the drive of the fan.

The fan 1 according to the first preferred embodiment has been described above. In the fan 1, the upper space 61, which is arranged between the upper seal portion 61 a and an inside of the rotor holder 121, is joined to the lower space 62 through the connection channel 51. A difference in pressure between the upper and lower spaces 61 and 62 can thus be reduced or eliminated. This contributes to preventing the lubricating oil 47 from leaking out of the upper and lower seal portions 61 a and 62 a. Provision of the thrust cap 45 between the lower space 62 and a space downstream of the fan 1 contributes to more effective prevention of occurrence of a difference in pressure between the upper and lower spaces 61 and 62.

FIG. 6 is a horizontal cross-sectional view illustrating a holder 46 according to a modification of the first preferred embodiment. The holder 46 includes a plurality of connection channel defining portions 5 defined therein. Each of the connection channel defining portions 5 is arranged to define a connection channel 51. The connection channels 51 are arranged at regular intervals in the circumferential direction. Provision of the plurality of connection channels 51 leads to more secure prevention of occurrence of a difference in pressure between an upper space 61 and a lower space 62 illustrated in FIG. 2.

FIG. 7 is a cross-sectional view of a bearing mechanism 401 according to a modification of the first preferred embodiment. A holder 46 includes a connection channel defining portion 5 a arranged to define a connection channel 51 a. The connection channel 51 a includes a vertical groove 514, an upper horizontal hole 512, and a lower horizontal hole 513. The vertical groove 514 is arranged to extend in the vertical direction in an outer circumferential surface of the holder 46 on a radially inner side of a stator 32. The vertical groove 514 and an inner circumferential portion of a stator core 321 are arranged to together define a vertical hole 514 a, which is a portion of the connection channel 51 a. The vertical groove 514 is arranged to connect the upper and lower horizontal holes 512 and 513 with each other.

The upper horizontal hole 512 is arranged to extend in a radial direction through the holder 46 on an upper side of the vertical groove 514. A radially inner end opening of the upper horizontal hole 512 is defined in a middle portion of an inner circumferential surface 46 a of the holder 46, and is joined to an upper seal gap 611. The lower horizontal hole 513 is arranged to extend in the radial direction through the holder 46 on a lower side of the vertical groove 514. A radially inner end opening of the lower horizontal hole 513 is defined in a lower portion of the inner circumferential surface 46 a of the holder 46, and is joined to a lower seal gap 621.

In the bearing mechanism 401, provision of the connection channel 51 a contributes to preventing occurrence of a difference in pressure between an upper space 61 and a lower space 62. In the case of the bearing mechanism 401, the vertical groove 514, the upper horizontal hole 512, and the lower horizontal hole 513 can be defined easily by moving a portion of a mold radially outward when the holder 46 is molded by a resin injection molding process.

FIG. 8 is a cross-sectional view of a bearing mechanism 401 according to another modification of the first preferred embodiment. In FIG. 8, the shape of a portion of the bearing mechanism 401 beyond a cross section of the bearing mechanism 401 is also depicted. The same is true of FIG. 9, which will be described below. A holder 46 includes a connection channel defining portion 5 b arranged to define a connection channel 51 b. The connection channel 51 b includes a holder groove 515 and a holder through hole 516. The holder groove 515 is arranged to extend in the vertical direction in an outer circumferential surface of the holder 46 on a radially inner side of an inner circumferential surface of a stator 32. The holder through hole 516 is arranged to extend in the vertical direction through the holder 46, from a lower end of the holder groove 515 to a lower end of an outer circumferential portion of the holder 46. The holder groove 515 and the inner circumferential surface of the stator 32 are arranged to together define a portion of the connection channel 51 b.

The holder through hole 516 is arranged radially outward of a thrust cap 45. A portion of the holder 46 which is radially outward of the thrust cap 45 includes a groove portion 516 a arranged to extend in the axial direction continuously from a lower end of the holder through hole 516. The groove portion 516 a is arranged to define a portion of the connection channel 51 b between the holder 46 and the thrust cap 45. A portion of the connection channel 51 b is defined between the groove portion 516 a and an outer circumferential surface of the thrust cap 45.

The thrust cap 45 includes a cap through hole 451 arranged to extend in the vertical direction through the thrust cap 45. When the bearing mechanism 401 is manufactured, a lubricating oil 47 is injected into the bearing mechanism 401 through the cap through hole 451.

An inner circumferential portion of a stator core 321 includes a cut portion 321 a arranged to extend in the vertical direction. When a plurality of magnetic steel sheets are placed one upon another to define the stator core 321, the cut portion 321 a may be used for circumferential positioning of each of the magnetic steel sheets. In the bearing mechanism 401, the cut portion 321 a and the holder groove 515 are arranged to overlap with each other in a radial direction. Note that the holder groove 515 may not necessarily be arranged to overlap with the cut portion 321 a of the stator core 321 in the radial direction, and that the holder groove 515 may be arranged to overlap with another portion of the inner circumferential portion of the stator core 321 in the radial direction.

In the bearing mechanism 401, an upper space 61, which includes a space above a surface of the lubricating oil 47 in an upper seal gap 611, is joined to a lower space 62 through the connection channel 51 b, a below-cap space 622, and the cap through hole 451, and this contributes to preventing occurrence of a difference in pressure between the upper and lower spaces 61 and 62.

FIG. 9 is a cross-sectional view of a bearing mechanism 401 according to yet another modification of the first preferred embodiment. FIG. 10 is a cross-sectional view of a holder 46 taken along line B-B in FIG. 9. The holder 46 includes a connection channel defining portion 5 c arranged to define a connection channel 52. The connection channel 52 is a vertical hole extending in the vertical direction. A radially inner portion of the connection channel 52 includes a slit-like portion arranged to extend in the vertical direction (hereinafter referred to as a “slit portion 521”).

As illustrated in FIG. 10, the circumferential width of the slit portion 521 is arranged to be considerably smaller than the circumferential width of a portion of the connection channel 52 which is radially outward of the slit portion 521. As illustrated in FIG. 9, the connection channel 52 is arranged to join a portion of an upper seal gap 611 which is above an upper seal portion 61 a to a portion of a lower seal gap 621 which is below a lower seal portion 62 a. This contributes to preventing occurrence of a difference in pressure between an upper space 61 and a lower space 62. In the bearing mechanism 401, the slit portion 521 is arranged to have a sufficiently small circumferential width to prevent entry of a lubricating oil 47 into the connection channel 52.

Second Preferred Embodiment

FIG. 11 is a diagram illustrating a fan 1 according to a second preferred embodiment of the present invention. A thrust cap 45 of the fan 1 includes a cap through hole 451 arranged to extend in the vertical direction through the thrust cap 45. A base portion 31 includes a base through hole 312 arranged to extend in the vertical direction through the base portion 31. A circuit board 33 includes a board through hole 332 arranged to extend in the vertical direction through the circuit board 33. The base through hole 312 and the board through hole 332 are arranged to coincide with each other when viewed in the axial direction. Note that these through holes 312 and 332 may not necessarily be arranged to coincide with each other when viewed in the axial direction.

An upper portion of a holder 46 includes a horizontal hole 517 arranged to extend in a radial direction therethrough. A radially inner end opening of the horizontal hole 517 is defined in an inner circumferential surface of an upper contact portion 463. The horizontal hole 517 is joined to an upper seal gap 611 through an airway 651. In the fan 1, one end portion of a tube 16 made of a resin is inserted into the horizontal hole 517 through a circumferential gap defined between adjacent coils 322 of a stator 32. The tube 16 is inserted through the board through hole 332 and the base through hole 312, and an opposite end portion of the tube 16 is inserted into the cap through hole 451. The fan 1 according to the second preferred embodiment is otherwise similar in structure to the fan 1 according to the first preferred embodiment.

In the second preferred embodiment, because of provision of the tube 16, which is a connection channel defining portion, an upper space 61 and a lower space 62 are connected with each other, and this contributes to preventing occurrence of a difference in pressure between the upper and lower spaces 61 and 62. Prevention of the occurrence of a difference in pressure between the upper and lower spaces 61 and 62 leads to prevention of a leakage of a lubricating oil 47. The same is true of other preferred embodiments of the present invention described below.

Third Preferred Embodiment

FIG. 12 is a diagram illustrating a fan 1 a according to a third preferred embodiment of the present invention. A bearing mechanism 402 of the fan 1 a includes a shaft 41, a sleeve 44, a holder 7, a thrust plate 42, a thrust cap 45, and a lubricating oil 47. The shaft 41 is inserted in the sleeve 44. The sleeve 44 is a sintered body impregnated with the lubricating oil 47. The thrust plate 42 is fixed to a lower end portion of the shaft 41.

The holder 7 includes a first holder 71 and a second holder 72. The first holder 71 is arranged substantially in the shape of a cylinder centered on a central axis J1, and is arranged to hold the sleeve 44. Each of an outer circumferential surface of the sleeve 44 and an outer circumferential surface of the thrust plate 42 is covered by the first holder 71. That is, an inner circumferential surface of the first holder 71 is arranged radially outside the outer circumferential surface of the sleeve 44 and the outer circumferential surface of the thrust plate 42. The first holder 71 includes an annular portion 711 arranged to project radially inward on an upper side of the sleeve 44. The portion 711 will be hereinafter referred to as an “annular upper portion 711”.

The second holder 72 is arranged substantially in the shape of a cylinder centered on the central axis J1. An outer circumferential surface of the first holder 71 is fixed to an inner circumferential surface of the second holder 72. A stator 32 is fixed to an outer circumferential surface of the second holder 72. The second holder 72 includes a connection channel defining portion 73 arranged to define a connection channel 730. The fan 1 a is similar in structure to the fan 1 according to the first preferred embodiment except in the structure of the bearing mechanism 402. Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted.

A radial bearing portion 66 a is defined in a radial gap 66 defined between an inner circumferential surface of the sleeve 44 and an outer circumferential surface of the shaft 41. On an upper side of the radial gap 66, an upper seal gap 611 is defined between an inner circumferential surface of the annular upper portion 711 and the outer circumferential surface of the shaft 41. The upper seal gap 611 is arranged to gradually increase in radial width with increasing height. An upper seal portion 61 a arranged to retain the lubricating oil 47 is defined in the upper seal gap 611. An upper surface of the lubricating oil 47 is defined in the upper seal portion 61 a. A lower seal gap 621 is defined between an inclined surface 421 of the thrust plate 42 and a lower portion of the inner circumferential surface of the first holder 71. The lower seal gap 621 is arranged to gradually increase in radial width with decreasing height. A lower seal portion 62 a arranged to retain the lubricating oil 47 is defined in the lower seal gap 621. A lower surface of the lubricating oil 47 is defined in the lower seal portion 62 a.

Referring to FIG. 13, a minute gap 74 extending in the axial direction is defined between an upper portion of the outer circumferential surface of the first holder 71 and an upper portion of the inner circumferential surface of the second holder 72. The minute gap 74 is joined to the upper seal portion 61 a through a horizontal gap 652 defined between a lower surface of a bushing 125 and an upper surface of the annular upper portion 711. The upper seal gap 611, the minute gap 74, the horizontal gap 652, and a vertical gap 653 defined between an outer circumferential surface of the bushing 125 and the upper portion of the inner circumferential surface of the second holder 72, that is, a space enclosed by the shaft 41, the holder 7, and a rotor holder 121, will be hereinafter referred to collectively as an “upper space 61”. Note that the upper space 61 may include a space defined between the rotor holder 121 and an inner circumferential portion of the stator 32.

The connection channel 730 includes a vertical hole 731, an upper horizontal hole 732, and a lower horizontal hole 733. The vertical hole 731 is arranged to extend in the vertical direction in the second holder 72. The upper horizontal hole 732 is arranged to extend radially inward from a top portion of the vertical hole 731. An end opening of the upper horizontal hole 732, i.e., an upper end opening of the connection channel 730, is defined in the upper portion of the inner circumferential surface of the second holder 72, and is joined to the minute gap 74.

The thrust cap 45 is fixed to a lower portion of the second holder 72. An inner circumferential portion of the second holder 72 includes a groove portion arranged to extend in the radial direction on an upper side of the thrust cap 45. This groove portion is arranged to define the lower horizontal hole 733 between the thrust cap 45 and the inner circumferential portion of the second holder 72. The lower horizontal hole 733 is arranged to extend radially inward from a bottom portion of the vertical hole 731. An end opening of the lower horizontal hole 733, i.e., a lower end opening of the connection channel 730, is defined in a lower portion of the inner circumferential surface of the second holder 72. A lower space 62 is defined by a combination of the thrust cap 45, the thrust plate 42, the holder 7, and the shaft 41.

In the third preferred embodiment, the upper space 61, which is arranged between the upper seal portion 61 a and an inside of the rotor holder 121, is connected with the lower space 62 through the connection channel 730, and this contributes to preventing occurrence of a difference in pressure between the upper and lower spaces 61 and 62.

FIG. 14 is a cross-sectional view of a bearing mechanism 402 according to a modification of the third preferred embodiment. A second holder 72 includes a connection channel defining portion 73 a arranged to define a connection channel 730 a. The connection channel 730 a includes a vertical groove 734 and a vertical hole 735. The vertical groove 734 is defined in an outer circumferential surface of the second holder 72. The vertical groove 734 and an inner circumferential surface of a stator 32 are arranged to together define a vertical hole which is continuous with the vertical hole 735 above the vertical hole 735. The vertical hole 735 is arranged to extend in the vertical direction through an outer circumferential portion of the second holder 72 on a lower side of the vertical groove 734. A thrust cap 45 includes a cap through hole 451 arranged to extend in the vertical direction through the thrust cap 45. A seal member 311 is attached to a lower surface of a base portion 31, so that a below-cap space 622 is defined below the thrust cap 45. A lower space 62 is joined to an upper space 61 through the cap through hole 451, the below-cap space 622, and the connection channel 730 a in a manner similar to that illustrated in FIG. 8.

Fourth Preferred Embodiment

FIG. 15 is a diagram illustrating a fan 1 b according to a fourth preferred embodiment of the present invention. The fan 1 b includes a rotating portion 2 a, a stationary portion 3 a, and a bearing mechanism 403. The bearing mechanism 403 includes a shaft 41, a bearing portion 49, a thrust plate 42, and a thrust cap 45. The bearing portion 49 includes a tubular sleeve 491 and a holder 492. The holder 492 is arranged to cover an outer circumferential surface of the sleeve 491. The shaft 41 is inserted in the sleeve 491. The thrust plate 42 is fixed to a lower end portion of the shaft 41. An upper surface of the thrust plate 42 is arranged axially opposite a lower surface of the sleeve 491. In the bearing mechanism 403, a lower seal portion 62 a is defined between an outer edge portion of the thrust plate 42 and a lower end portion of the holder 492. A lower surface of a lubricating oil 47 is defined in the lower seal portion 62 a. A lower space 62 is defined by a combination of the thrust plate 42, the bearing portion 49, and the thrust cap 45.

A rotor holder 121 a of the rotating portion 2 a includes a first rotor member 126 and a second rotor member 127. The first rotor member 126 includes a thrust portion 126 b. The thrust portion 126 b is arranged in a substantially annular shape centered on a central axis J1, and is arranged to extend radially outward from an upper portion of the shaft 41. The second rotor member 127 is attached to an outer circumferential surface of the first rotor member 126. The second rotor member 127 includes a cylindrical portion 127 a. A rotor magnet 22 is fixed to an inner circumferential surface of the cylindrical portion 127 a. Blades 122 are arranged on an outer circumferential surface of the cylindrical portion 127 a.

The first rotor member 126 further includes a rotor cylindrical portion 126 a. The rotor cylindrical portion 126 a is a cylindrical portion arranged to extend axially downward from the thrust portion 126 b on a radially outer side of the holder 492. An upper seal gap 611 is defined between an inner circumferential surface of the rotor cylindrical portion 126 a and an upper portion of an outer circumferential surface of the holder 492. The upper seal gap 611 is arranged to gradually increase in radial width with decreasing height. An upper seal portion 61 a is defined in the upper seal gap 611. A surface of a lubricating oil 47 is defined in the upper seal portion 61 a.

The stationary portion 3 a includes a substantially cylindrical bushing 31 a. The bushing 31 a is arranged to extend upward from a central portion of a base portion 31. The bushing 31 a and the base portion 31 are defined by a single member. On a lower side of the thrust plate 42, the thrust cap 45 is fixed to a lower portion of the bushing 31 a, and a lower opening of the bushing 31 a is closed by the thrust cap 45. A stator 32 is fixed to an outer circumferential surface of the bushing 31 a. The holder 492 is fixed to an inner circumferential surface of the bushing 31 a. The bushing 31 a includes a projecting portion 313 and a connection channel defining portion 34 arranged to define a connection channel 340. The projecting portion 313 is arranged to extend upward on a radially outer side of the rotor cylindrical portion 126 a. A vertical gap 655 arranged to extend in the axial direction is defined between the rotor cylindrical portion 126 a and the projecting portion 313, and this contributes to preventing evaporation of the lubricating oil 47 out of the upper seal portion 61 a. The holder 492 includes a recessed portion, which is recessed radially inward, defined in a middle portion of the outer circumferential surface thereof. The vertical gap 655 is joined to the upper seal gap 611 through a space 623 enclosed by the recessed portion of the holder 492, a lower portion of the rotor cylindrical portion 126 a, and a portion of the bushing 31 a which is radially inward of the projecting portion 313. The vertical gap 65, the space 623, and the upper seal gap 611 (more precisely, a space below the surface of the lubricating oil 47 in the upper seal gap 611) will be hereinafter referred to collectively as an “upper space 61”.

The connection channel 340 includes a vertical hole 341 and a lower horizontal hole 342. The vertical hole 341 is arranged to extend in the axial direction on a radially inner side of the projecting portion 313. An upper end opening of the vertical hole 341 is joined to the upper space 61. The thrust cap 45 is fixed to the lower portion of the bushing 31 a. An inner circumferential portion of the bushing 31 a includes a groove portion shaped like a cut and arranged to extend in a radial direction on an upper side of the thrust cap 45. This groove portion is arranged to define the lower horizontal hole 342 between the thrust cap 45 and the inner circumferential portion of the bushing 31 a. The lower horizontal hole 342 is arranged to extend radially inward from a lower end of the vertical hole 341. An end opening of the lower horizontal hole 342, i.e., a lower end opening of the connection channel 340, is defined in the inner circumferential surface of the bushing 31 a. The lower space 62 is joined to the lower horizontal hole 342.

In the bearing mechanism 403, an upper thrust bearing portion 661 a, which is arranged to support the first rotor member 126 in the axial direction, is defined in an upper thrust gap 661 defined between a lower surface of the thrust portion 126 b and an upper surface of the sleeve 491. The first rotor member 126 thus plays a part in defining the upper thrust bearing portion 661 a. A lower thrust bearing portion 662 a, which is arranged to support the thrust plate 42 in the axial direction, is defined in a lower thrust gap 662 defined between the lower surface of the sleeve 491 and the upper surface of the thrust plate 42. A radial bearing portion 66 a, which is arranged to support the shaft 41 in the radial direction, is defined in a radial gap 66 defined between an outer circumferential surface of the shaft 41 and an inner circumferential surface of the sleeve 491.

In the fourth preferred embodiment, in a manner similar to that of the first preferred embodiment, the upper space 61, which is arranged between the upper seal portion 61 a and an inside of the rotor holder 121 a, is connected with the lower space 62, which is arranged above the thrust cap 45, through the connection channel 340, and this contributes to preventing occurrence of a difference in pressure between the upper and lower spaces 61 and 62. Note that, in a modification of the bearing mechanism 403, the upper thrust bearing portion may be defined between the first rotor member 126 and an upper surface of the holder 492. The same is true with the case of FIG. 16, which will be described below.

FIG. 16 is a cross-sectional view of a bearing mechanism 403 according to a modification of the fourth preferred embodiment. A connection channel 340 a defined by a connection channel defining portion 34 a of a bushing 31 a includes a bushing groove 343 and a bushing through hole 344. The bushing groove 343 is arranged to extend in the vertical direction in an outer circumferential surface of the bushing 31 a on a radially inner side of an inner circumferential surface of a stator 32. The bushing through hole 344 is arranged to extend in the vertical direction through an outer circumferential portion of the bushing 31 a from a lower end of the bushing groove 343 to a lower end of the outer circumferential portion of the bushing 31 a. More precisely, the bushing groove 343 and the inner circumferential surface of the stator 32 are arranged to together define a vertical hole which is continuous with the bushing through hole 344 above the bushing through hole 344. A thrust cap 45 includes a cap through hole 451. A below-cap space 622 is defined between the thrust cap 45 and a seal member 311 attached to a lower surface of a base portion 31 below the thrust cap 45.

In the bearing mechanism 403, a lower space 62 is connected with an upper space 61 through the cap through hole 451, the below-cap space 622, and the connection channel 340 a.

FIG. 17 is a diagram illustrating a bearing mechanism 403 according to another modification of the fourth preferred embodiment. The bearing mechanism 403 includes a bearing portion 493, which is a single sleeve made of a metal. An outer circumferential surface of the bearing portion 493 is fixed to a bushing 31 a. A radial bearing portion 66 a is defined in a radial gap 66 defined between an inner circumferential surface of the bearing portion 493 and an outer circumferential surface of a shaft 41, which is inserted in the bearing portion 493. An upper thrust bearing portion 661 a is defined in an upper thrust gap 661 defined between an upper surface of the bearing portion 493 and a lower surface of a first rotor member 126. Note that the bearing mechanism 403 does not include a lower thrust bearing portion. The bearing mechanism 403 according to the present modification of the fourth preferred embodiment is otherwise similar in structure to the bearing mechanism 403 of the fan 1 b illustrated in FIG. 15. In the case also of FIG. 17, because of provision of a connection channel 340, an upper space 61 and a lower space 62 are connected with each other, and this contributes to preventing occurrence of a difference in pressure between the upper and lower spaces 61 and 62.

While preferred embodiments of the present invention have been described above, it is to be understood that the present invention is not limited to the above-described preferred embodiments, and that a variety of modifications are possible. For example, in a modification of the bearing mechanism 401 illustrated in FIG. 2, a portion of the holder 46 which is on an upper side of the upper horizontal hole 512, a portion of the holder 46 which is on a lower side of the lower horizontal hole 513, and a portion of the holder 46 which is arranged between the above two portions and includes the connection channel defining portion 5 may be defined by separate members. In this case, the connection channel defining portion 5 can be defined more easily.

In a modification of the third preferred embodiment, a tube 16 may be arranged to join the upper and lower spaces 61 and 62 to each other. The same is true of a modification of the fourth preferred embodiment. In a modification of the fan 1 a illustrated in FIG. 12, a groove portion arranged to extend in the vertical direction and define a connection channel may be defined in the inner circumferential surface of the second holder 72. The same is true of each of modifications of the bushings 31 a illustrated in FIGS. 15 and 17, respectively.

Features of the above-described preferred embodiments and the modifications thereof may be combined appropriately as long as no conflict arises.

The present invention is applicable to fans arranged to produce air currents. 

What is claimed is:
 1. A fan comprising: a plurality of blades; and a motor arranged to rotate the blades about a central axis; wherein the motor includes: a stationary portion including a stator; a rotating portion including a rotor magnet arranged radially outside the stator; and a bearing mechanism arranged to support the rotating portion such that the rotating portion is rotatable with respect to the stationary portion; the rotating portion includes a rotor holder arranged in a shape of a covered cylinder, and including an outer circumferential surface on which the blades are arranged; the bearing mechanism includes: a shaft; a sleeve in which the shaft is inserted; a holder arranged to hold the sleeve; and a thrust plate fixed to a lower end portion of the shaft on a lower side of the sleeve; the shaft and the sleeve are arranged to together define a radial gap therebetween, the radial gap including a radial bearing portion arranged to support the shaft in a radial direction; the thrust plate and the holder are arranged to together define a lower seal portion therebetween, the lower seal portion having a lower surface of a lubricating oil defined therein, while the holder and the sleeve are arranged to together define an upper seal portion therebetween, the upper seal portion having an upper surface of the lubricating oil defined therein; and the holder includes a connection channel defining portion arranged to define a connection channel to connect an upper space defined between the upper seal portion and an inside of the rotor holder with a lower space at which the lower seal portion is arranged.
 2. The fan according to claim 1, wherein a lower surface of the sleeve and an upper surface of the thrust plate are arranged to together define a lower thrust gap therebetween, the lower thrust gap including a lower thrust bearing portion arranged to support the thrust plate in an axial direction.
 3. The fan according to claim 1, wherein an outer circumferential surface of the sleeve and an inner circumferential surface of the holder are arranged to together define an upper seal gap therebetween, the upper seal gap being arranged to gradually increase in radial width with increasing height, the upper seal gap including the upper seal portion defined therein; and the upper space is a space enclosed by the sleeve, the holder, the shaft, and the rotor holder.
 4. The fan according to one of claims 1 and 3, wherein an upper end opening of the connection channel defining portion is defined in the inner circumferential surface of the holder.
 5. The fan according to one of claims 1 and 3, wherein a lower end opening of the connection channel defining portion is defined in the inner circumferential surface of the holder.
 6. The fan according to one of claims 1 and 3, wherein the bearing mechanism further includes a thrust cap arranged to close a lower opening of the holder; and the lower space is arranged on an upper side of the thrust cap.
 7. The fan according to claim 6, wherein the thrust cap includes a cap through hole arranged to extend in a vertical direction through the thrust cap; and the lower space is connected with the upper space through the cap through hole and the connection channel.
 8. The fan according to claim 7, further comprising a seal member arranged on a lower side of the thrust cap to define a space between the thrust cap and the seal member, wherein the connection channel includes: a holder groove arranged to extend in the vertical direction in an outer circumferential surface of the holder on a radially inner side of an inner circumferential surface of the stator; and a holder through hole arranged to extend through the holder from the holder groove to a lower end of the holder; and the lower space is connected with the upper space through the cap through hole, the space defined between the thrust cap and the seal member, the holder through hole, and the holder groove.
 9. The fan according to any one of claims 1 to 3, wherein a plurality of connection channel defining portions are provided; and each of the connection channel defining portions is arranged to define one of a plurality of connection channels arranged at regular intervals in a circumferential direction.
 10. A fan comprising: a plurality of blades; and a motor arranged to rotate the blades about a central axis; wherein the motor includes: a stationary portion including a stator; a rotating portion including a rotor magnet arranged radially outside the stator; and a bearing mechanism arranged to support the rotating portion such that the rotating portion is rotatable with respect to the stationary portion; the rotating portion includes a rotor holder arranged in a shape of a covered cylinder, and including an outer circumferential surface on which the blades are arranged; the bearing mechanism includes: a shaft; a sleeve in which the shaft is inserted; a holder arranged to hold the sleeve; and a thrust plate fixed to a lower end portion of the shaft on a lower side of the sleeve; the holder includes: a cylindrical first holder arranged to cover an outer circumferential surface of the sleeve and an outer circumferential surface of the thrust plate, the first holder including an annular upper portion arranged to project radially inward on an upper side of the sleeve; and a second holder including an inner circumferential surface having an outer circumferential surface of the first holder fixed thereto, the second holder having the stator arranged on a radially outer side thereof; the shaft and the sleeve are arranged to together define a radial gap therebetween, the radial gap including a radial bearing portion arranged to support the shaft in a radial direction; the thrust plate and the first holder are arranged to together define a lower seal portion therebetween, the lower seal portion having a lower surface of a lubricating oil defined therein, while the shaft and the annular upper portion are arranged to together define an upper seal portion therebetween, the upper seal portion having an upper surface of the lubricating oil defined therein; and the second holder includes a connection channel defining portion arranged to define a connection channel to connect an upper space defined between the upper seal portion and an inside of the rotor holder with a lower space at which the lower seal portion is arranged.
 11. The fan according to claim 10, wherein a lower surface of the sleeve and an upper surface of the thrust plate are arranged to together define a lower thrust gap therebetween, the lower thrust gap including a lower thrust bearing portion arranged to support the thrust plate in an axial direction.
 12. The fan according to claim 10, wherein an inner circumferential surface of the annular upper portion and an outer circumferential surface of the shaft are arranged to together define an upper seal gap therebetween, the upper seal gap being arranged to gradually increase in radial width with increasing height, the upper seal gap including the upper seal portion defined therein; and the upper space is a space enclosed by the shaft, the holder, and the rotor holder.
 13. The fan according to any one of claims 10 to 12, wherein an upper end opening of the connection channel defining portion is defined in the inner circumferential surface of the second holder.
 14. The fan according to any one of claims 10 to 12, wherein a lower end opening of the connection channel defining portion is defined in the inner circumferential surface of the second holder.
 15. The fan according to any one of claims 10 to 12, wherein the bearing mechanism further includes a thrust cap arranged to close a lower opening of the holder; and the lower space is arranged on an upper side of the thrust cap.
 16. The fan according to claim 15, wherein the thrust cap includes a cap through hole arranged to extend in a vertical direction through the thrust cap; and the lower space is connected with the upper space through the cap through hole and the connection channel.
 17. The fan according to claim 16, further comprising a seal member arranged on a lower side of the thrust cap to define a space between the thrust cap and the seal member, wherein the connection channel includes: a holder groove arranged to extend in the vertical direction in an outer circumferential surface of the second holder on a radially inner side of an inner circumferential surface of the stator; and a holder through hole arranged to extend through the second holder from the holder groove to a lower end of the second holder; and the lower space is connected with the upper space through the cap through hole, the space defined between the thrust cap and the seal member, the holder through hole, and the holder groove.
 18. The fan according to any one of claims 10 to 12, wherein a plurality of connection channel defining portions are provided; and each of the connection channel defining portions is arranged to define one of a plurality of connection channels arranged at regular intervals in a circumferential direction.
 19. A fan comprising: a plurality of blades; and a motor arranged to rotate the blades about a central axis; wherein the motor includes: a stationary portion including a stator; a rotating portion including a rotor magnet arranged radially outside the stator; and a bearing mechanism arranged to support the rotating portion such that the rotating portion is rotatable with respect to the stationary portion; the stationary portion includes a bushing arranged to hold the stator on a radially outer side thereof; the rotating portion includes a rotor holder arranged in a shape of a covered cylinder, and including an outer circumferential surface on which the blades are arranged; the bearing mechanism includes: a shaft; a bearing portion in which the shaft is inserted; a thrust plate fixed to a lower end portion of the shaft on a lower side of the sleeve; a thrust portion arranged to extend radially outward from an upper portion of the shaft; and a rotor cylindrical portion arranged to extend axially downward from the thrust portion; the shaft and the bearing portion are arranged to together define a radial gap therebetween, the radial gap including a radial bearing portion arranged to support the shaft in a radial direction; the thrust plate and the bearing portion are arranged to together define a lower seal portion therebetween, the lower seal portion having a lower surface of a lubricating oil defined therein, while the bearing portion and the rotor cylindrical portion are arranged to together define an upper seal portion therebetween, the upper seal portion having an upper surface of the lubricating oil defined therein; and the bushing includes a connection channel defining portion arranged to define a connection channel to connect an upper space defined between the upper seal portion and an inside of the rotor holder with a lower space at which the lower seal portion is arranged.
 20. The fan according to claim 19, wherein a lower surface of the bearing portion and an upper surface of the thrust plate are arranged to together define a lower thrust gap therebetween, the lower thrust gap including a lower thrust bearing portion arranged to support the thrust plate in an axial direction.
 21. The fan according to one of claims 19 and 20, wherein the bearing portion includes: a tubular sleeve; and a holder arranged to cover an outer circumferential surface of the sleeve; and an upper surface of the sleeve and a lower surface of the thrust portion are arranged to together define an upper thrust bearing portion therebetween, the upper thrust bearing portion being arranged to support the thrust portion in an axial direction.
 22. The fan according to one of claims 19 and 20, wherein a lower end opening of the connection channel defining portion is defined in an inner circumferential surface of the bushing.
 23. The fan according to one of claims 19 and 20, wherein the bearing mechanism further includes a thrust cap arranged to close a lower opening of the bushing; and the lower space is arranged on an upper side of the thrust cap.
 24. The fan according to claim 23, wherein the thrust cap includes a cap through hole arranged to extend in a vertical direction through the thrust cap; and the lower space is connected with the upper space through the cap through hole and the connection channel.
 25. The fan according to claim 24, further comprising a seal member arranged on a lower side of the thrust cap to define a space between the thrust cap and the seal member, wherein the connection channel includes: a bushing groove arranged to extend in the vertical direction in an outer circumferential surface of the bushing on a radially inner side of an inner circumferential surface of the stator; and a bushing through hole arranged to extend through the bushing from the bushing groove to a lower end of the bushing; and the lower space is connected with the upper space through the cap through hole, the space defined between the thrust cap and the seal member, the bushing through hole, and the bushing groove.
 26. The fan according to one of claims 19 and 20, wherein a plurality of connection channel defining portions are provided; and each of the connection channel defining portions is arranged to define one of a plurality of connection channels arranged at regular intervals in a circumferential direction. 